Former Prime Minister Gordon Brown delivers a speech on the impact of the no vote in Scottish referendum at Dalgety Bay Primary School in Fife. Photograph: Tolga Akmen/LNP

His last speech on the eve of the Scottish independence referendum electrified his audience, brought passion to the no campaign and, some say, may even have saved the union. Four days on from his accurate forecast that the "silent majority" would be silent no more, Gordon Brown was back.

This time there were jokes, some of them self-deprecating ("I know a little about resignations after you've lost a vote," he said dryly, in response to Alex Salmond's retirement) and there was little of the angry passion of his performance at Maryhill's Community Centre Hall in Glasgow. "Two days after a divisive vote, it is not time for barnstorming speeches," he said.

In its place, once the ice-breaking jokes were done, was reflection and grim resolve: he was not making a comeback and he was "too young" to be an elder statesman, but Brown would not allow the "promise-makers" of the independence referendum campaign to become "promise-breakers", he told his audience in Fife.

The three party leaders, who had promised so much in terms of new powers for the Scottish parliament if the people voted no to independence, were firmly in his sights. "The eyes of the world have been upon us and now I think the eyes of the world are on the leaders of the major parties of the United Kingdom," Brown said. "These are men who have been promise-makers and they will not be promise-breakers.

"I will ensure that as a promise keeper that these promises that have been made will be upheld. We will lock in today the promises that have been made and when the timetable we set out will be delivered. Action has already been taken to make sure that happens."

It is, perhaps, of no surprise that the Scottish media now calls Brown the "fourth man" of British politics, alongside David Cameron, Nick Clegg and Ed Miliband. In the past week, events and the force of his personality have made this the case. On Saturday, he did nothing to dissuade people from the impression that he is Scotland's enforcer, making sure that Scotland receives what it is owed.

Brown said he had signed a resolution, to be placed in the Commons on Monday, along with the three party leaders committing the government to living up to its promises of devolution. And he'd taken the "unusual" step of personally contacting the civil service to make sure it was now working on proposals around which the parties could unite.

Fears have been raised that party political discord over the pace at which constitutional reform across the UK should take place could result in failure to live up to promises to the Scots. Miliband has refused to sign up to the prime minister's view that devolution to Scotland should happen at the same time as parliamentary reform to ensure that English laws were made only by English MPs. And over the weekend the government's chief whip, Michael Gove, insisted that Scottish devolution could not go ahead unless it went hand-in-glove with changes to the Commons. "It would be impossible to move forward without making sure you have change both in Scotland and in England," Gove had told the Times.

But Brown assured Scots that none of this would wash on his watch. This timetable to further Scottish devolution, nothing less than "a modern version of home rule", was "self-contained and unaffected by anything else happening elsewhere", he said.

He added: "We have set down a timetable that is absolutely clear. That a command paper will be published by the end of October, that the heads of agreement between the parties and further devolution will come in November and that the draft legislation, the laws that will form the Scotland bill and eventually the Scotland Act, will be ready by the end of January. If you like, by St Andrew's Day the heads of agreement, and by Burns Day the laws that we will then enact for the future of the country."

But for all the former prime minister's apparent desire to have taken on the retiring SNP leader Alex Salmond's role of holding "Westminster's feet to the fire" over their promises, Brown also showed a statesman-like touch that perhaps the first minister lacks

Brown, the MP for Kirkcaldy and Cowdenbeath, who said both former US president Bill Clinton and former UN secretary general Kofi Annan had offered him congratulations over the no victory, appealed for Scotland to move beyond the threats, abuse and recriminations of recent days. In a reference to his father's role as a church minister, Brown told the audience: "The Old Testament says that there is a time for everything and a season for every activity under the heavens. And we know from the psalms that there is a time to tear down and a time to build. A time to tear up and a time to mend. As they put it: 'A time to kill and a time to heal'.

"I would put it in modern language: there is a time to fight and a time to unite, and from today onwards this is the time to unite. Not just in words, but in deeds, and around what I know we can discover as a common purpose for our country … Let us also stop allowing our flag to be used as a weapon against opponents, and let us make our flag a national symbol of what unites all of us, as we – all of us – stand together." It was, he said, time for the next stage of Scotland's journey. Many in the audience wondered what their speaker's next step would be too.